Asexual propagation for plants has been shown for some species to yield large numbers of genetically identical embryos, each having the capacity to develop into a normal plant. Such embryos must usually be further cultured under laboratory conditions until they reach an autotrophic “seedling” state characterized by an ability to produce their own food via photosynthesis, resist desiccation, produce roots able to penetrate soil, and fend off soil microorganisms. Some researchers have experimented with the production of artificial seeds, known as manufactured seeds, in which individual plant somatic or zygotic embryos are encapsulated in a seed coat. Examples of such manufactured seeds are disclosed in U.S. Pat. No. 5,701,699, issued to Carlson et al., the disclosure of which is hereby expressly incorporated by reference.
Typical manufactured seeds include a seed shell, synthetic gametophyte and a plant embryo. A manufactured seed that does not include the plant embryo is known in the art as a “seed blank.” The seed blank typically is a cylindrical capsule having a closed end and an open end. The synthetic gametophyte is placed within the seed shell to substantially fill the interior of the seed shell. A longitudinally extending hard porous insert, commonly known as a cotyledon restraint, may be centrally located within the synthetic gametophyte and includes a centrally located cavity extending partially through the length of the cotyledon restraint. The cavity is sized to receive the plant embryo therein. The well-known plant embryo includes a radicle end and a cotyledon end. The plant embryo is deposited within the cavity of the cotyledon restraint cotyledon end first and is sealed within the seed blank by at least one end seal. There is a weakened spot in the end seal to allow the radicle end of the embryo to penetrate the end seal.
Currently, the seed shell is manufactured by hand and is formed from sectioning a tube, such as a straw, and processing the sections of the tube to enhance its abilities to withstand exposure to the environment. One such seed shell is manufactured by sectioning a straw of fibrous material, and then coating the resulting straw section with a wax. One suitable method for applying the wax coating is to dip the straw sections into a bath of wax. The straw sections are then withdrawn from the wax bath and then the wax is permitted to harden to seal the straw sections.
Delivery of the plant embryo within the seed coat has utilized a liquid-based transport system to move the plant embryo through the manufactured seed production line. In such a liquid-based transport system, plant embryos are placed in a container of liquid to orient them in a like direction. The plant embryos are caused to float to the top of the container, such that each embryo floats upwardly within the container cotyledon end first. From the top of the container, additional liquid is used to propel the plant embryos out of the container while maintaining their cotyledon end first orientation. Liquid is then used to transport the plant embryos through the remaining manufactured seed production line steps. The embryos are hand selected and inserted into the seed coat. Thereafter, the embryo is sealed within the seedcoat resulting in a manufactured seed suitable for planting.
Although such manufacturing systems are effective at producing manufactured seeds, they are not without their problems. As a non-limiting example, because such manufacturing systems are predominately human controlled, they are expensive, labor intensive, and relatively slow at mass producing manufactured seeds.
Thus, there exists a need for a method and system of producing manufactured seeds that is capable of reliably producing a large number of manufactured seeds at a relatively low cost, and minimizing the risk of damaging or contaminating the plant embryo.